The present invention relates to a device for dispensing a liquid. The invention is particularly useful for delivering medicaments at predetermined rates, and is therefore described below, with respect to this application.
There are many applications requiring the dispensing or delivering of a liquid at predetermined or precisely controlled rates. One of the applications requiring particularly precise rates of delivery are systems for administering insulin or other medicaments, and very precise pumps have been devised for this purpose. However, such pumps are expensive to produce and maintain, and are inconvenient to refill with the periodic dosage requirements.
It has been proposed, particularly in such applications, to use as the liquid dispensing device a container for receiving a supply of the liquid to be dispensed, and an arrangement for subjecting the liquid to a pressurized gas to force the liquid from the container. Examples of such known systems are illustrated in U.S. Pat. No. 3,640,277 disclosing a gas cartridge for supplying the gas pressure, U.S. Pat. No. 3,468,308 disclosing an inflated bladder for supplying the gas pressure, and U.S. Pat. No. 3,871,553 connectable to a compressed air hose for supplying the air pressure. All such known arrangements, however, require a valve which must be precisely controlled in order to control the rate of delivery of the liquid to be dispensed. Such precise control is extremely difficult when very low rates of delivery are required as in the case of delivery of insulin or other types of medicaments.